Hot topics in adeno-associated virus as a gene transfer vector

Evaluation of a Serum-free Medium for the Production of rAAV-2 using HeLa Derived Producer Cells

During the last decade, recombinant AAVs have become of increasing interest for gene therapy. Clinical trials have been conducted following promising in vivo evaluations, thus leading laboratories to adapt their production systems for larger and higher quality demands. Classical transfection protocols seem difficult and cumbersome to adapt to a bioreactor scale. The use of stable producer cells appears as an attractive alternative, as this system requires only a single infection step to induce rAAV production. Furthermore, the switch to a serum-free medium is an interesting strategy to increase the biosafety level to satisfy clinical grade requirements for gene therapy products. Here, we have combined both approaches and evaluated different rAAV producer clones in a serum-free medium. We first evaluated the cell growth in a serum-free medium and then did a partial optimisation of the medium composition to obtain vector yields as close as possible to the yields obtained in a classical serum containing medium. Different helper viruses, multiplicity of infection, times of infection and harvest have been compared in small scale cultures in order to determine the optimal settings which were then transferred and evaluated in suspension cultures in spinner flasks. The yields obtained in this system were similar to or at most 2 times lower than those obtained in a serum-containing medium. The scale-up of such a production system as well as the use of high cell density perfusion culture systems will probably lead to considerably higher yields than those obtained in a classical process.

Chitosan Interferon-gamma Nanogene Therapy for Lung Disease: Modulation of T-Cell and Dendritic Cell Immune Responses

The use of chitosan nanoparticles as carriers for expression plasmids represents a major improvement in gene expression technology. We demonstrated previously that treatment with chitosan interferon-γ (IFN-γ) plasmid deoxyribonucleic acid (DNA) nanoparticles (chitosan interferon-γ nanogene [CIN]) led to in situ production of IFN-γ and a reduction in inflammation and airway reactivity in mice, but the mechanism underlying the immunomodulatory effects of CIN remains unclear. In this report, the effect of CIN treatment on the immune responses of CD8⁺ T cells and dendritic cells was examined in a BALB/c mouse model of ovalbumin (OVA)-induced allergic asthma. OT1 mice (OVA-T cell receptor [TCR] transgenic) were also used to test the effects of CIN on OVA-specific CD8⁺ T cells. CIN treatment caused a reduction in IFN-γ production in a subpopulation of OVA-specific CD8⁺ T cells cultured in vitro in the presence of OVA. CIN also reduced apoptosis of the CD8⁺ T cells. Examination of dendritic cells from lung and lymph nodes indicated that CIN treatment decreased their antigen-presenting activity, as evident from the reduction in CD80 and CD86 expression. Furthermore, CIN treatment significantly decreased the number of CD11c⁺b⁺ dendritic cells in lymph nodes, suggesting that endogenous IFN-γ expression may immunomodulate dendritic cell migration and activation. CIN therapy results in a reduction in proinflammatory CD8⁺ T cells and decreases the number and antigen-presenting activity of dendritic cells.

Preparation of poly(ethylene glycol)-introduced cationized gelatin as a non-viral gene carrier

The objective of this study was to prepare cationized gelatins grafted with poly(ethylene glycol) (PEG) (PEG-cationized gelatin) and evaluate the in vivo efficiency as a non-viral gene carrier. Cationized gelatin was prepared by chemical introduction of ethylenediamine to the carboxyl groups of gelatin. PEG with one terminal of active ester group was coupled to the amino groups of cationized gelatin to prepare PEG-cationized gelatins. Electrophoretic experiments revealed that the PEG-cationized gelatin with low PEGylation degrees was complexed with a plasmid DNA of luciferase, in remarked contrast to that with high PEGylation degrees. When the plasmid DNA complexed with the cationized gelatin or PEG-cationized gelatin was mixed with deoxyribonuclease I (DNase I) in solution to evaluate the resistance to enzymatic degradation, stronger protection effect of the PEG-cationized gelatin was observed than that of the cationized gelatin. The complex of plasmid DNA and PEG-cationized gelatin had an apparent molecular size of about 300 nm and almost zero surface charge. These findings indicate that the PEG-cationized gelatin-plasmid DNA complex has a nano-order structure where the plasmid DNA is covered with PEG molecules. When the PEG-cationized gelatin-plasmid DNA complex was intramuscularly injected, the level of gene expression was significantly increased compared with the injection of plasmid DNA solution. It is concluded that the PEG-cationized gelatin was a promising non-viral gene carrier to enhance gene expression in vivo.

Use of localised gene transfer to develop new treatment strategies for the salivary component of Sjögren's syndrome

Effective treatment for Sjögren's syndrome (SS) might be developed locally by introducing genes encoding cytokines, which are potentially anti-inflammatory, or by introducing a cDNA encoding a soluble form of a key cytokine receptor, which can act as an antagonist and decrease the availability of certain cytokines, such as soluble tumour necrosis factor alpha receptors. Currently, the preferred choice of viral vector for immunomodulatory gene transfer is recombinant adeno-associated virus. The use of gene transfer to help determine the pathophysiology and to alter the course of the SS-like disease in the NOD mouse model can ultimately lead to the development of new treatments for managing the salivary component in patients with SS.

Immune responses to adeno-associated virus and its recombinant vectors

Recombinant adeno-associated virus (rAAV) vectors have emerged as highly promising for use in gene transfer for a variety of reasons, including lack of pathogenicity and wide host range. In addition, all virus-encoded genes have been removed from standard rAAV vectors, resulting in their comparatively low intrinsic immunogenicity. For gene replacement strategies, transgenes encoded by rAAV vectors may induce less robust host immune responses than other vectors in vivo. However, under appropriate conditions, host immune responses can be generated against rAAV-encoded transgenes, raising the potential for their use in vaccine development. In this review, we summarize current understanding of the generation of both undesirable and beneficial host immune responses directed against rAAV and encoded transgenes, and how they might be exploited for optimal use of this promising vector system.

Dystrophic phenotype of canine X-linked muscular dystrophy is mitigated by adenovirus-mediated utrophin gene transfer

Utrophin is highly homologous and structurally similar to dystrophin, and in gene delivery experiments in mdx mice was able to functionally replace dystrophin. We performed mini-utrophin gene transfer in Golden Retriever dogs with canine muscular dystrophy (CXMD). Unlike the mouse model, the clinicopathological phenotype of CXMD is similar to that of Duchenne muscular dystrophy (DMD). We injected an adenoviral vector expressing a synthetic utrophin into tibialis anterior muscles of newborn dogs affected with CXMD and examined transgene expression by RNA and protein analysis at 10, 30 and 60 days postinjection in cyclosporin-treated and -untreated animals. Immunosuppression by cyclosporin was required to mitigate the immune response to viral and transgene antigens. RT-PCR analysis showed the presence of the exogenous transcript in the muscle of cyclosporin-treated and -untreated animals. The transgenic utrophin was efficiently expressed at the extrajunctional membrane in immunosuppressed dogs and this expression was stable for at least 60 days. We found reduced fibrosis and increased expression of dystrophin-associated proteins (DAPs) in association with muscle areas expressing the utrophin minigene, indicating that mini-utrophin can functionally compensate for lack of dystrophin in injected muscles. For this reason, utrophin transfer to dystrophin-deficient muscle appears as a promising therapeutic approach to DMD.

Gene transfer approaches for the treatment of inflammatory bowel disease

The pathogenesis of Crohn's disease and ulcerative colitis, the two major forms of inflammatory bowel disease, involves a complex interplay between certain genetic, environmental and immunological factors. Considerable research progress in the last decade defined key inflammatory pathways in the inflamed gut and identified new potential therapeutic targets. Since the current medical treatment with corticosteroids and anti-inflammatory drugs is often associated with undesired side effects and cannot completely cure IBD, these current advances in our understanding of intestinal pathology may now allow the development of new biologic treatment strategies including gene therapy. In this review, we will give a brief overview of potential gene therapy target molecules related to chronic intestinal inflammation. Furthermore, we summarize the results of recent preclinical studies for intestinal gene transfer and discuss future perspectives.